Impact blow actuated pneumatic fastener driving device



United States Patent [72] Inventor Granville R. Hedrick Memphis, Tennessee [21] Appl. No. 729,095

[22] Filed May 14,1968

[45] Patented Nov. 24,1970

[7 3] Assignee Textron Inc.

Providence, Rhode Island a corporation ol' Delaware [54] IMPACT BLOW ACTUATED PNEUMATIC FASTENER DRIVING DEVICE l l l l l Primary Examiner-Granville Y. Custer, Jr. Attorney-Cushman` Darby & Cushman ABSTRACT: A tluid pressure operated fastener driving device provided with an external impact blow receiving member connected through a mechanical motion-transmitting mechanism to the main valve means of the device which controls the communication of source air pressure with the driving chamber to effect the driving stroke of the fastener driving elementA An impact blow applied to the'impact blow receiving member serves to open the main valve means in direct response to the impact blow. Preferably, the impact blow receiving member is positioned in longitudinal alignment with the fastener driving element and moves in the same direction as the drive stroke of the fastener driving element when impacted. The application of the impact blow serves to preposition the workpiece before the fastener is driven, to provide a quicker opening ofthe main valve means, to aid in the fastener driving operation and to dissipate recoil action.

Patented Nov. 24, 1970 3,542,273

BMM, @/m ATTORNI; YS

I NVE NTOR Patented` Nov. 24, 1970 ATTORNEYS IMPACT BLOW ACTUATED PNEUMATIC FASTENER DRIVING DEVICE Fluid pressure operated fastener driving devices have been available commercially for many years. The commercial usage of such devices has increased over the years and along with this increased usage the operating efficiency of such devices has also been improved. Such devices conventionally include a fastener driving element which is moved through a drive stroke by a piston mounted within a cylinder. A magazine structure is provided for receiving and supporting a supply of fasteners and for feeding a fastener from this supply into a position to be engaged by the fastener driving element during the drive stroke of the latter and to be driven thereby into a workpiece.

In the early years of the commercial development of the devices of this type, the source of compressed air to move the drive piston was controlled by a Single trigger valve which, when moved into an open position directly in response to the depression of a trigger by the operator served to communicate the source of compressed air with the interior of the cylinder to effect the drive stroke of the piston. While devices of this type performed satisfactorily in commercial operation they did not make the most efficient use of the source of cornpressed air available because of the lag in communicating the pressure source to the interior of the cylinder after the main valve was opened due to the relatively tortuous path of communication between the main valve when opened and the interior of the cylinder. With an arrangement of this type full source pressure was not immediately available to commence the drive stroke ofthe piston.

ln the more recent commercial embodiments o'f devices of this type, the driving efficiency has been greatly improved by providing a substantially direct communication between the source of compressed air and the interior of the cylinder. See for example, Goldring et al. U.S. Pat. No. 3,081,742 dated Mar. I9. l963, which discloses a reservoir surrounding the upper end of the drive cylinder to which a source of cornpressed air is continuously communicated and a main control valve which, in one position, engages the upper end of the cylinder to close off communication of the interior thereof with the reservoir and in a second position permits direct communication of the reservoir pressure with the interior of the cylinder. An arrangement of this type eliminates to a substantial extent the tortuous path of communication between the pressure source and the interior of the cylinder present in previous devices thus making full source pressure immediately available to the interior of the cylinder and effecting a more effecient driving stroke ofthe piston.

Since the advent of the main valve arrangement such as disclosed in the aforementioned Goldring patent, there have been proposed both commercially and in the patented literature numerous variations in the main valve structure as well as the relationship of the main valve with respect to the reservoir and interior of the cylinder. However, a common charac teristic of all ofthese variations is that the main valve is moved into opened and closed positions by air pressure controlled by secondary valve means. the latter usually being actuated manually as by a trigger and/or a contact trip element.

The present invention is based upon the principle that the fastener driving efficiency of a device of the type described can be still furtherimproved by effecting a mechanical movement ofthe main control valve from its closed position into its opened position in response to an impact blow rather than in response to change in pressure conditions resulting from the actuation of secondary valve means. This improved efficiency is achieved by the'more rapid opening of the main control valve by means of an impact blow as distinguished from a change in air pressure conditions. It will be understood that source pressure will be more rapidly available to effect the drive stroke ofthe piston where the main valve is more rapidly moved into its fully opened position.

Accordingly, it is an object of the present invention to provide a fluid pressure operated device of the type described having means for rapidly effecting a mechanical movement of the main control valve into its opened position in response to an impact blow applied to an impact blow receiving member carried by the device.

In accordance with the principles ofthe present invention. it has been found that the driving efficiency of a fluid pressure actuated fastener driving device can be improved sufficiently that the drive stroke will take place substantially simultaneously with the impact blow which is applied to initiate the drive stroke. Consequently, in accordance with the present invention, it is preferable that the initiating impact blow be applied to the device in a direction which is substantially the same as the direction in which the fastener is driven` Under these circumstances, the initiating impact blow aids in the fastener driving operation and has the effect of substantially reducing the recoil action heretofore experienced in prior art devices.

Accordingly, it is a further object of the present invention to provide a fluid pressure operated device of the type described in which the impact blow receiving member which serves to open the main valve to initiate the drive stroke is positioned so that the initiating impact blow received thereby will be transmitted to the device in substantially the same direction as the fastener is driven.

While the principles of the present invention may be embodied in a device so as to constitute the sole means of opening the main valve to initiate the drive stroke of the piston, the present invention contemplates the application of these principles to existing devices in such a way that the operator is provided with an independent alternate means of actuating the main valve in addition to the conventional actuation means provided, as for example, fluid pressure actuation of the main control valve through secondary control valve means operated in response to digital movement of a trigger and/or in response to workpiece engagement ofa contact trip element.

Accordingly, it is an object of the present invention to provide a fluid pressure actuated device of the type described having means for mechanically moving the main control valve means into an open position to effect the drive stroke of the piston in response to the application of an impact blow to an impact blow receiving member carried by the device, which device also includes as an alternate means for opening the main valve, secondary control valve means through which the main control valve is opened in response to a change in air pressure conditions acting thereon.

These and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.

The invention may best be understood by reference to the accompanying drawings wherein an illustrative embodiment is shown.

IN THE DRAWINGS:

FIG. 1 is a perspective view of a fluid pressure operated fastener driving device embodying the principles of the present invention;

FIG. 2 is an enlarged vertical sectional view taken along the line 2-2 of FIG. I, showing the parts in their normal inoperative position; i

FIG. 3 is a view similar to FIG. 2 showing the parts in their impact blow actuated position; and

FIG. 4 is a sectional view taken along the line 4-4 of FIG.

Referring now more particularly to the drawings, there is shown therein a fluid pressure operated fastener driving device, generally indicated at 10, which embodies the principles ofthe present invention. The device shown constitutes a conventional fastener driving device produced commercially by Bostitch Division of Textron Inc. under the trade name Mark Il, modified to embody the principles of the present in vention. lt will be understood, however, that while the principles of the present invention may be readily incorporated in this existing fastener driving device, the present invention is equally applicable to other devices of this type as well as devices specifically developed to embody the present inven tion. The specific structure of the conventional elements which form a part of the novel combination of the present invention can be varied, as desired.

Since the device l includes many structural elements which are not modified in accordance with the principles of the present invention, the present description will be primarily concerned with the modifications of the conventional structure which have been effected to incorporate the features of the present invention therein. lt will be understood that a detailed understanding of the structure and mode of operation of the unmodified conventional structure can be had by reference to commonly assigned U.S. Pat. to Smith No. 3,051,135 dated Aug. 28, 1962A As best shown in FIGS l3, device l0 includes a main rigid housing structure, generally indicated at 12, which includes a body portion 14, an integral handle portion 16, a fixed nosepiece portion 18 defining a drive track 20, a magazine assembly 22 fixed to the nosepiece portion 18 and cooperating with the drive track to feed the leading fastener of a fastener stick contained therein to the drive track.

The body portion 14 of the housing structure 12 includes a main driving cylinder 24 within which a driving piston 26 is mounted for movement between the ends thereof. At the end of the cylinder remote from the nosepiece portion 18 there is provided an inwardly directed flange 28, the lower inner peripheral portion of which defines a valve seat forming a part ofa main control valve means, generally indicated at 30.

The main control valve means 30 includes an annular valve member 32 which is mounted for movement between a first position ofengagement with the valve seat of flange 28 which closes off communication between the adjacent end of the cylinder 24 and an air pressure reservoir 34 defined by the interior of the body portion adjacent the cylinder 24 and the interior of the handle portion 16 and a second position spaced from the valve seat defined by the flange 28 permitting communication between the reservoir and the adjacent end ofthe cylinder 24. As shown in the drawings, the reservoir 34 is adapted to be continuously communicated with a source of pressure (not shown) through a line 36 or the like.

The main valve member 32 is in the form of an annular ring of resilient material mounted within a peripheral groove formed within the lower end of an elongated hollow member 38 which extends upwardly through the fiange 28 and has a piston portion 40 fixedly secured to the upper end portion thereof. The piston portion 40 is slidably mounted within a pilot pressure control chamber 42, the inner end of which communicates with the reservoir 34, as by a central opening 44.

The outer end of the chamber 42 is closed by a closure cap 46 which, in accordance with the principles of the present invention, is modified to include a cylindrical opening 48 concentric with the hollow member 38 and the cylinder 24. The opening 48 is formed with an annular groove to receive annular sealing means, such as an O-ring seal 50 or the like. In accordance with the principles of the present invention, the piston portion 40 is modified to include integral cylindrical portion 52 extending outwardly through the opening 48 in sliding sealing engagement with the O-ring 50. As best shown in FlGS. 2 and 3, the outer extremity of the cylindrical portion 52 has its exterior periphery formed to engage within a socket 54 formed in one end ofan impact blow receiving member 56.

Piston portion 40 and the adjacent part of the cylindrical portion 52 have a central opening 58 formed therein which communicates with the adjacent end of the hollow member 38. ln the embodiment shown, the piston portion 40 together with the integral outwardly extending cylindrical portion 52 constitute a separate piece from the hollow member 38 but these pieces are fixedly secured together in rigid relation as by a plurality of bolts 60,

As best shown in FIG. 4, the opening 58 is communicated with the chamber 42 by any suitable means, such as a plurality ofcircumferentially spaced radially extending ports 62 formed in the part of the cylindrical portion 52 adjacent the piston portion 40.

The main control valve member 32 is moved between its first and second positions by introducing air under pressure from the reservoir into the pilot pressure control chamber 42 and exhausting air under pressure from the chamber 42. This action is accomplished by means of a secondary valve means, generally indicated at 64, which is normally biased into a first position closing a port 66 which serves to communicate the reservoir with the chamber 42 through a passage 68. Also` in its normally biased first position, the secondary valve means 64 serves to exhaust the chamber 42 to atmosphere through a port 70 which is positioned between the passage 68 and an exhaust passage 72. The secondary valve means 64 is moved from its normally biased first position into a second position by a pivoted trigger 74 wherein port 66 is opened and port 70 is closed.

The detailed structure and mode of operation of the secondary valve means 64 is fully disclosed in the aforementioned Smith patent to which reference may be had if neces: ary. Briefly, it will be noted that when the secondary valve means is disposed in its normally biased first position, cham ber 42 is exhausted to atmosphere and the fluid pressure within the reserA voir 34 acts on the piston portion 40 through the opening 44 to bias the piston portion and hence the valve member 32 fixed thereto into engagement with the valve seat defined by the flange 28. lt will be noted that the reservoir pressure acts on a surface area which is equal to the difference between the area of the piston portion 40 less the area of the valve member 32 inwardly of its engagement with the valve seat in a direction to close the valve.

When the secondary valve means 64 is moved into its second position by digital actuation ofthe trigger 74, reservoir pressure is communicated with the chamber 42. This pressure acts on an effective area which is equal to the difference between the area ofthe main valve inwardly of its engagement with the valve seat and the area of the closure cap opening 48 which effective area is greater than the effective area in communication with the reservoir. Consequently, the main valve member 32 is moved into its opened second position in response to the movement of the secondary valve means into its second position.

When the main control valve member 32 is moved into its opened second position, reservoir pressure immediately communicates with the adjacent end ofthe cylinder and acts upon the drive piston 26 to move the latter from a fastener receiving position through its drive stroke into a fastener driven position. During this movement, a fastener driving element 76 fixed to the piston and extending through the drive track 20 serves to engage the leading fastener positioned within the drive track through the operation ofthe fastener magazine 22, to strip the fastener from the fastener stick, and to drive the fastener outwardly ofthe drive track into a workpiece.

As disclosed in the aforementioned Smith patent, the device 10 includes a pneumatic return means, generally indicated at 78, which serves to effect movement of the piston from its fastener driven position through a return stroke into its fastener receiving position in response to the movement of the secondary valve means 64 from its second position into its first position which in turn closes the main valve means 30.

The pneumatic return means 78 includes a tubular member 80 fixed at one end to the piston 26 extending therefrom into the hollow member 38 and having a piston portion 82 formed on the opposite end thereof in sliding sealing engagement with the interior of the hollow member 38. The end of the tubular member 80 adjacent the piston portion 82 is thus communicated with the chamber 42 and its opposite end is communicated with the cylinder 24 by means of a plurality of circumferentially spaced radially extending apertures 84. Mounted interiorly within the hollow member 38 at a position adjacent the valve member 32 is an annular sealing means, such as an O-ring 86, which slidably sealingly engages the exterior periphery of the tubular member 80 in spaced relation to the piston portion 82. The O-ring seal 86 and piston portion 82 define an annular air return chamber 88 which is communicated at all times with the reservoir as by a plurality of circumferentially spaced radially extending apertures 90 formed in the hollow member 38.

lt will be understood that the reservoir pressure acting on the piston portion 82 within the annularchamber 88 after the main valve 32 has closed, serves to effect the movement ofthe piston 26 through its return stroke. During the return stroke, the air pressure within the cylinder 24, which has accomplished the drive stroke and is trapped therein due to the closing of the main valve, is allowed to exhaust to atmosphere along with the pressure within chamber 42 through the apertures 84 and the interior of the tubular member 80. ln this way, the fastener driving element 76 of the present device is moved through its drive stroke and its return stroke in response to the digital actuation of the trigger 74 and release thereof by an operation which is as disclosed in the aforementioned Smith patent.

However, in accordance with the principles of the present invention, the modifications of the device to include the impact blow receiving member 56 and the cylindrical portion 52 integral with the piston portion 40, permits the fastener driving element 76 to be moved through a drive stroke and a return stroke in response to the application of an impact blow, as by a mallet, or a hammer or the lkejdesignated by the letter M in FIG. 1. The device 10 modified to embody the principles of the present invention is thus capable of being actuated both in response to an impact blow and conventionally by the actuation ofthe trigger 74 at the option of the operator.

IMPACT BLOW ACTUATED OPERATION When the impact blow receiving member S6 is struck by the mallet M, the cylindrical portion 52, piston portion 40, and hollow member 38 act as a motion-transmitting mechanism which transmits the impact movement of the impact blow receiving member 56 to the main valve member 32 thus moving the latter from its first position in engagement with the valve seat defined by the flange 28 into its opened position communicating the reservoir pressure with the adjacent end of the cylinder so as to effect the drive stroke of the piston 26. ln this regard, it will be noted that the force of the impact blow is sufficient to overcome the air pressure bias of the main valve member 32 and that this movement of the main valve is instantaneously responsive to the impact blow. Indeed, this responsive movement of the main valve into an opened position occurs more rapidly than' the opening of the main valve in response to the introduction of reservoir pressure into the chamber 42 following the movement of the secondary valve means into its second position when the trigger is digitally actuatedA ln this way, reservoir pressure is rapidly communicated to the adjacent end of the cylinder and immediately acts on the piston to move the latter and hence the fastener driving element 76 through a drive stroke, It will be noted that during this movement some of the reseroir pressure entering the cylinder is free to dissipate through the aperture 84 and the chamber 42 which is communicated with atmosphere through the port 70 and passage 72 by virtue of the fact that the secondary valve means 64 is in its normally biased first position. Nevertheless, any pressure dissipation is insignificant and has no material effe-f.I on the efficiency ofthe drive stroke.

The rapid opening movement of the main valve in response to the impact blow causes the drive stroke of the piston to occur almost simultaneously with the opening of the main valve so that the impact blow, which is applied in the same direction as the direction of the drive stroke ofthe fastener driving element 76, aids in the driving of the fastener into the workpiece and further serves to dissipate any recoil action which might occur. Immediately after the impact blow has been applied` the reservoir pressure bias on the main valve will cause the latter to return to its closed first position. Since the secondary valve means 46 is already disposed in its normally biased first position, the return stroke of the piston is immediately effected in the manner previously described.

lt will be noted that with the present arrangement the main valve 32 is moved into its opened position in response to the impact blow in the same direction in which the impact blow receiving member is moved by the application of the impact blow itself. While an arrangement of this type is preferable, it will be understood that where the main valve is moved into opened position in a direction opposed to the direction of movement ofthe impact blow receiving member when the irnpact blow is applied thereto, a reversing motion transmitting mechanism can be utilized. lt is greatly preferred that the irnpact blow receiving member be mounted so as to move in the same direction as the direction of movement of the fastener driving element through its drive stroke, an optimum position of the impact blow receiving member being in longitudinal alinement with the fastener driving element 76, although it is within the contemplation of the invention to position the impact blow receiving member at locations other than one of longitudinal alinement with the fastener driving element.

While the present invention has general utility in the fastener driving art, it is particularly suited to the use of fastener driving devices in installing flooring and the like, as for example, tongue and groove boards B as shown in FIG, i. ln such usage, the impact blow which is applied to actuate the device can also be used to insure a tight tongue and groove engagement of the board B through which the fastener is driven.

Where the device 10 is to be used particularly for flooring installation, a board-engaging fixture generally indicated at 94, is preferably attached under the nosepiece portion 18 and the adjacent part of the magazine assembly 22, in accordance with conventional practice. An embodiment of such a fixture is illustrated in FIGS. 1--3 ofthe drawing which includes a bottom wall 96 having a board engaging pad 98 detachably secured to the lower surface thereof. At one end ofthe pad 98. the bottom wall extends downwardly to provide a gauge portion 100, the bottom wall extending horizontally from the lower end of the gauge portion to provide a support portion 102.

Extending upwardly from opposite sides of the bottom wall is a pair of generally triangularly shaped sidewalls 104, the upper edges of which are connected by a top wall 106 disposed at an angle of approximately 45with respect to the bottom wall 96. The top wall 106 is provided with an aperture 108 to receive the nosepiece portion 18 and adjacent part of the magazine assembly 22. The fixture 94 is detachably secured to the device 10 by means of bolts 110, which serve to secure the nosepiece portion of the device to the body portion of the housing structurefln the juncture between the guide portion and support portion 102, the bottom wall 96 is provided with an opening 112 in alinement with the opening 108 to receive the nosepiece portion 18 of the device. ln addition, a transverse wall 114 is provided between the sidewalls 104 in a position to be engaged by the bottom of the adjacent part ofthe magazine assembly 22.

lt will be noted that the fixture 94 serves to retain the device in a 45incline with respect to the horizontal when the device is in use with the lower surface of the pad 98 positioned on the upper surface of the boards B and the guide portion 100 in engagement with the upper portion of the free edge of the board above the tongue thereof. ln this relationship, the fastener driving element 76 is disposed so as to drive the fastener in a I45"angle through the board in the juncture of the tongue with the top edge of the board.

For the additional convenience of the operator, an auxiliary handle attachment 116 of conventional construction may be utilized, if desired. As shown, such auxiliary handle at` tachment includes a generally L-shaped handle member 118 providing a generally horizontally extending upper handle portion and generally upright leg portion the lower end of which is rigidly secured to an L-shaped bracket 120. The L- shaped Bracket is secured to the exterior of the handle portion 16 ofthe housing structure by a pair of L-shaped bolts 122 having threadly mounted on each end thereof nuts 124,

The intensity of the impact blow applied to the impact blow receiving member by the operator is, of course, considerably less than that required to actually drive the fastener into the workpiece. The intensity is more in the nature of that required to insure a firm tongue and groove engagement of the board being nailed. Since in the normal installation of flooring the installer will usually apply blows to the board being nailed, the operation of the present device simplifies installation notwithstanding the fact that more effort is required to actuate the device by an impact blow than is required to digitally actuate the trigger. The device of the present invention provides an overall improvement in the operation because the actuating impact blow is not only utilized to insure a tight tongue and groove engagement of the board being fastened but serves as well to aid in the fastener driving operation and to dissipate any recoil action in the manner previously described.

lt thus will be seen that the objects of this invention have been fully and effectively accomplished. lt will be realized, however, that the foregoing specific embodiment has been shown and described only for the purpose of illustrating the I principles of this invention and is subject to extensive change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope ofthe following claims.

lclaim:

l. A fluid pressure operated fastener driving device comprising:

a rigid housing structure including a body portion, a handle portion fixed with respect to said body portion adapted to be manually gripped-by an operator to move said device into an operative position to drive a fastener into a workpiece, and a nosepiece portion fixed with respect to said body portion adapted to be directed toward the workpiece when the device is moved into its operative position with respect thereto;

said body portion defining a longitudinally extending cylinder having spaced ends',

a piston mounted within said cylinder for movement from a fastener receiving position adjacent one end of said cylinder through a drive stroke into a fastener driven position adjacent the other end of said cylinder and from said fastener driven position through a return stroke into said fastener receiving position,

fastener driving means operatively connected with said piston for movement through a drive stroke when said piston is moved through its drive stroke and through a return stroke when said piston is moved through its return stroke;

means carried by said housing structure for receiving and supporting a supply of fasteners and for feeding the leading fastener from such supply into a position to be driven by said fastener driving means during the drive stroke of the latter;

said housing structure defining a reservoir disposed generally in close communicating relation with said one end of'said cylinder for receiving and containing a continuous supply ofair under pressure;

main valve means mounted within said housing structure for movement between a first position closing communication between said reservoir and the interior of said cylinder adjacent said one end and a second position communicating said reservoir with the interior of said cylinder adjacent said one end thereof;

said piston being movable through its drive stroke in response to the movement of said valve means from said first position into said second position through the action of air under pressure within said reservoir communicating with the interior of said cylinder adjacent said one end thereofand being movable through its return stroke when said valve means is moved from said second position into said first position;

an impact blow receiving member mounted exteriorly of said housing structure for movement from a first position into a second position in response to the application of an impact blow thereto; and

mechanical motion-transmitting means operatively connecting said impact blow receiving member with said main valve means for effecting movement of said main valve means from said first position into said second position in response to the movement of said impact blow receiving member from its first position into its second position through the application of an impact blow thereto; and

said impact blow receiving member and said main valve means being operable to move from the second positions thereof to the first positions thereof after the impact blow has been applied to said impact blow receiving member.

2. A fluid pressure operated fastener driving device as defined in claim l wherein said impact blow receiving member is mounted so as to move generally in the same direction as the direction of movement of said fastener driving means during its drive stroke when moved from said first position to said second position in response to the application of an impact blow thereto so that the latter will aid in the fastener driving action of said fastener driving means and generally dissipate a recoil action of the device thereto.

3. A fluid pressure operated fastener driving device as defined in claim 2 wherein said impact blow receiving member is alined longitudinally with respect to said cylinder.

4. A fluid pressure operated fastener driving device as defined in claim 1 wherein said main valve means is operable to be biased by air under pressure into one of said positions and includes pressure surface means operable when communicated with air under pressure from said reservoir to effect movement of said main valve means from said one position thereof into the other position thereof and secondary valve means manually operable to control ine communication of air under pressure from said reservoir to the pressure surface means of said main valve means so as to effect movement of the latter between the first and second positions thereof independent ofthe application of an impact blow to said impact blow receiving member.

5. A fluid pressure operated device as defined in claim 4 including digitally engageable trigger means for operating said secondary valve means.

6. A fluid pressure operated fastener driving device as defined in claim 1 wherein said main valve means includes a main valve member mounted within the one end portion of said cylinder disposed in closing relation to the one end of said cylinder when in said first position and being movable in a direction the same as the direction the drive stroke of said piston when moved from said first position into said second position and wherein said mechanical motion-transmitting means comprises a rigid structure connected fixedly with said main valve member and fixedly with said impact blow receiving member and extending longitudinally therebetween.

7. A fluid pressure operated fastener driving device as defined in claim 6 wherein said rigid motion transmitting structure includes a cylindrical portion extending through said housing structure and annular seal means operatively mounted between said cylindrical portion and the portion of said housing structure through which said cylindrical portion extends.

8. A fluid pressure operated fastener driving device as defined in claim 7 wherein said rigid motion transmitting structure further includes a piston portion disposed inwardly of said cylindrical portion, said housing structure defining a chamber slidably receiving said piston portion, said chamber opening to said reservoir adjacent one side of said piston portion to continuously communicate air under pressure from said reservoir to said one side of Said piston portion to thereby bias said piston portion in a direction to move said main valve member and said impact blow receiving member fixed thereto into the first positions thereof, the opposite side of said piston portion presenting a greater effective surface area than said one side thereof; and means independent of said impact blow receiving member for'controlling the introduction of air under pressure from said reservoir into said chamber in communication with tne opposite side of said piston portion to thereby bias said piston portion in a direction to move said main valve member and said impact blow receiving member fixed thereto into the second positions thereof and for controlling the exhaust of air under pressure from said chamber.

9. A fluid pressure operated fastener driving device as defined in claim 8 wherein said last mentioned means comprises secondary valve means mountedv for movement between a first position closing off communication between said reservoir and said chamber at the opposite side of said piston portion and communicating the latter to atmosphere and a second position permitting communication between said reservoir and said chamber at the opposite side ofsaid piston portion.

l0. A fluid pressure operated fastener driving device as defined in claim 9 wherein said main valve member is formed with a central opening therein, said rigid motion transmitting structure including a central opening extending longitudinally therein which communicates at one end with the central opening in said main valve member and at its opposite end with said chamber at the opposite side of said piston portion, a tubular member fixed to said and extending through the main valve opening into the opening in said rigid motion transmitting structure, the end of said tubular member adjacent said piston being interiorly communicated with the interior of said cylinder of the side of said piston adjacent said one end thereof, the opposite end of said tubular member communicating interiorly with said chamber at the opposite side of said piston portion so as to provide a path through said tubular member for the passage of air under pressure within thc one end portion of said cylinder into said chamber at the opposite side of said piston portion to be discharged to atmosphere when said secondary valve means is disposed in said first position, a portion of said tubular member extending into the central opening of said rigid motion transmitting structure defining an annular air return chamber, the opposite end of said tubular member having an annular portion defining one end of said air return chamber, annular sealing means defining the opposite end of said air return chamber, said rigid motion transmitting structure having an opening therein continu ausly communicating said air return chamber with said reservoir. 

